“Mainframe” originated from the physical frames of early computers like the IBM 701 (1952). Initially, it referred to the main part of a computer, later evolving to denote a large, powerful computer for transactions. The term’s meaning shifted in the 1970s to differentiate from minicomputers, and definitions transitioned in dictionaries over the decades. IBM was hesitant to use “mainframe” as a marketing term until the mid-1980s, after which the usage surged, peaking in the 1990s before declining. Despite predictions of obsolescence, mainframes persist today, and their terminology continues to evolve.
https://www.righto.com/2025/02/origin-of-mainframe-term.html